The present invention relates to an inkjet printer for forming an image on a print medium with an ink ejected from a recording head, and more particularly relates to an inkjet printer capable of measuring the amount of ink ejected from the recording head with high accuracy.
Inkjet printers have various advantages such as low cost, high print quality, and color printing capability, and have been widely used not only in offices, but also in ordinary homes with the spread of personal computers. Such an inkjet printer forms a printed image by depositing on a print medium an ink which is controllably ejected from a nozzle of a recording head in response to commands electronically transmitted to the recording head.
In order to realize high quality printing, it is necessary to always eject a constant amount of ink from the nozzle of the recording head during printing. However, since this nozzle has a very small diameter, the nozzle is sometimes clogged with dust or the like and does not eject the ink at all, or eject an incorrect amount of ink drops. In order to prevent such drawbacks, the invention of U.S. Pat. No. 6,278,469 determines the ink ejection capability of the recording head by using a sensor for detecting the flying condition of an ink drop, or an optical, piezoelectric or electrostatic impact sensor for measuring the pressure of an ink drop, and provides a print mask for controlling the amount of ink according to the determined capability.
According to the above-mentioned technique of U.S. Pat. No. 6,278,469, however, if the sensor is of an optical type, it is necessary to print a test pattern on a print medium when determining the ink ejection capability, and thus resulting in waste of the print medium. Moreover, since the piezoelectric/electrostatic sensor measures the pressure of an ink drop by an extremely weak signal, the S/N ratio is poor and there arises the problem that the amount of ink can not be measured accurately.